RATIONALE: Erlotinib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Giving erlotinib before surgery may make the tumor smaller and reduce the amount of normal tissue that needs to be removed. Drugs used in chemotherapy, such as capecitabine and gemcitabine, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Radiation therapy uses high-energy x-rays to kill tumor cells. Giving erlotinib together with combination chemotherapy and radiation therapy after surgery may kill any tumor cells that remain after surgery.